Lymphatic malformations (LMs) are congenital lesions affecting 1:3500 children usually manifesting in early childhood, and are associated with significant morbidities, including vision loss, respiratory failure, and repetitive infections. Whie LMs are increasingly identified antenatally, triggering perinatal interventions and intensive support of affected babies, they are frequently refractory to surgical and medical treatment. Notably, the pathobiology of LMs is poorly understood, and the processes governing response and recurrence have not been studied. In the United States, most LM patients are monitored with 2D magnetic resonance imaging (MRI), which is expensive, time-consuming, and requires anesthesia in children. MRI is therefore not feasible for real-time, rapid, serial monitoring of treatment responses in pediatric LM patients. Thus, the development of new noninvasive monitoring strategies is urgently needed. Ultrasound-based imaging has the potential to address this need, as it is quick, inexpensive, and can be implemented with equipment already widely available. We have recently isolated a novel stem cell-like population from LM patient samples (LMSCs). LMSCs form lesions which phenocopy clinical LMs, molecularly and by ultrasound and MRI, after implantation into immunodeficient mice. We propose to use this LM mouse model to develop an ultrasound-based diagnostic and monitoring tool for LMs, with the ultimate goal of testing and translating novel therapies. Specifically, we will evaluate the concurrent use of three acoustic methodologies: microultrasound, contrast- enhanced ultrasound (CEUS), and harmonic motion imaging (HMI), both on developing LMs and after pilot treatments with current agents. We will compare the data obtained with the results of parallel MR imaging, and correlate results with molecular and histologic characteristics. These pre-clinical studies are highly innovative and clinically relevant, and could provide a crucial platform for the rapid translation f new therapeutic approaches. Our overall goal is to enhance our ability to rigorously evaluate novel LM therapies, integrating clinically relevant imaging and a mechanistic understanding of LM pathogenesis. Such an approach would have high potential for improving care for this orphan disease of childhood. !